SOLUTION: A photographer has two bottles of developer, one a 70% solution, the other, 20% solution. How much developer should he take from each bottle to make 10 ounces of 50% solution?

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Question 1160380: A photographer has two bottles of developer, one a 70% solution, the other, 20% solution. How much developer should he take from each bottle to make 10 ounces of 50% solution?
Found 2 solutions by josgarithmetic, ikleyn:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
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...,bottles of developer, one a 70% solution, the other, 20% solution. How much developer should he take from each bottle to make 10 ounces of 50% solution?
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x of 70%
10-x of 20%

70x%2B20%2810-x%29=50%2A10
-
7x%2B2%2810-x%29=5%2A10
7x%2B2%2A10-2x=5%2A10
%287-2%29x%2B2%2A10=5%2A10
%287-2%29x=10%285-2%29
highlight_green%28x=10%28%285-2%29%2F%287-2%29%29%29

highlight%28x=6%29------------"ounces" of the 70% developer

highlight%284%29------------"ounces" of the 20% developer

Answer by ikleyn(52787) About Me  (Show Source):
You can put this solution on YOUR website!
.

I remember my father used "bottles of developer", when he worked on photographies at home in fifties last century,

but the contemporary people (and young people, especially and totally) simply don't know what is it . . .

It looks like your source is just at least 60 years old . . .